You can click the "Advanced" button to expand this section and show extra details. You can click the blue error message to expand this section. If the certificate is not trusted (SEC_ERROR_UNKNOWN_ISSUER) then click "Copy text to clipboard" and paste the base64 encoded certificate chain text in a reply. That will allow us to check details like the issuer of the certificate.

Hi there, Thank you for your question. If you do not mind, please share the website that is giving this error.

Do you also have an antivirus software or a firewall enabled on the Windows Computer?

Second, it is possible that you have a pending update to your operating system. Please make sure it is up to date.

Last, but not least, you can add the exception under the security certificate error. Does it go away after adding the exception?

What I think you are seeing is documented here: https://support.mozilla.org/en-US/kb/Certificate%20contains%20the%20same%...

If it does not let you add an exception, please post back and I can give you some new steps.

Did you add an exception in the past to this website?

You can check the Servers tab in the certificate manager.

• Options/Preferences -> Privacy & Security -> Certificates: View Certificates

Thank you all for your prompt responses! I hate coincidences, but my problem solved itself, and I think it was because dear Microsoft was messing with my computer. It was trying to install the latest big update, and failed with the install. That's about when I started having troubles. Eventually, I had to force a shutdown because it simply froze up. When I opened the computer the next day, the day of my question, it immediately began to try to update again, but I wasn't aware of it at the time. Today, after taking 24 hours for the update and reboots, everything is behaving normally. Sorry to have troubled you, and I truly appreciate your kindness! (I have an HP laptop, Window 10)